1. Field of the Invention
The present invention relates to an end-closing structure for an actuator for transferring workpieces.
2. Description of the Related Art
In recent years, various types of actuators have been used as means for transferring workpieces in a factory or the like.
The actuators convert a power generated by air or oil pressure into a power for the use of mechanical work by a cylinder tube and a piston received into a cylinder chamber of the cylinder tube for being displaced axially along the cylinder chamber, wherein the cylinder tube and the piston are closely fitted together. One type of the above actuators is a rodded cylinder, wherein a piston rod is exposed from a rod cover connected to an end of the cylinder tube. Another type of the above actuators is a rodless cylinder, wherein the space needed for attaching the actuator is reduced.
For example, the above rodless cylinder is constructed such that a driving power can be taken out from a slit of the cylinder tube through a yoke or the like. The structure and the operation thereof will be briefly explained below.
A rodless cylinder shown in FIG. 3 includes a bore 2 extending longitudinally in a cylinder tube 1 of a cylinder body. Each end of the cylinder tube 1 is closed in an airtight manner by a cover 4 which serves to close the end of the cylinder tube 1 having a shape of a rectangular parallelopiped. A fluid input/output port 3a is defined in the cover 4. A cylindrical piston 5 is provided in the cylinder tube 1. Pressure receiving surfaces 5a, 5b are formed at both ends of the piston 5. A yoke 6 protruding from a slit (not shown) is provided on the upper portion of the piston 5. Further, a movable body 7, which engages with the yoke 6, is provided such that the movable body 7 is displaced in unison with the yoke 6. The slit of the cylinder tube 1 is covered with a seal band 8a, and the yoke 6 is covered with a dust seal band 8b.
In the rodless cylinder constructed as above, the piston 5 reciprocates along the bore 2 by, for example, pressurized fluid such as compressed air supplied from the fluid input/output port 3a. In this case, the yoke 6 and the movable body 7 are displaced in unison with the piston 5 such that a workplace (not shown) placed on the movable body 7 is transferred to a predetermined position.
The structure of closing the end of the rodless cylinder by the cover 4 will be further explained.
As shown in FIG. 4, the cover 4 comprises a rectangular parallelopiped member 4a and a cylindrical member 4b. The cylindrical member 4b has a step which extends into an unillustrated hole of the rectangular parallelopiped member 4a. Thus, the rectangular parallelopiped member 4a and the cylindrical member 4b are connected. The fluid input/output port 3a is defined in the center of an end surface of the rectangular parallelopiped member 4a. The fluid input/output port 3a communicates with a hole 3c of the cylindrical member 4b through a passage 3b defined in the rectangular parallelopiped member 4a. Further, through holes 4c are defined in the rectangular parallelopiped member 4a for attaching the rodless cylinder to another member. The cylindrical member 4b is inserted into the bore 2 defined in the cylinder tube 1 by four bolts 9 which are screwed into holes defined adjacent to four corners of the rectangular parallelopiped member 4a, respectively. In this way, the cover 4 is fixed to the end of the cylinder tube 1, thereby closing the bore 2.
The cover 4 of the conventional rodless cylinder (actuator) adopts a construction, wherein the rectangular parallelopiped member 4a and the cylindrical member 4b in different shapes are connected, and a plurality of bolts 9 are needed for fixing the cover 4 to the end of the cylinder tube 1. Accordingly, both of manufacturing and attaching operations thereof are laborious, and, the manufacturing cost of the actuator becomes rather high. Further, since the cover 4 is fixed to the cylinder tube 1 such that the cover 4 protrudes outwardly from the end of the cylinder tube 1, the overall longitudinal dimension of the apparatus is equal to a sum of dimensions of the cylinder tube 1 and the covers 4. Accordingly, an actuator as a finished product tends to be unduly elongated.